The present invention relates to an internal combustion engine arrangement, and more specifically to such an arrangement comprising a waste heat recovery system.
For many years, attempts have been made to improve the efficiency of internal combustion engines, which has a direct impact on fuel consumption.
For this purpose, an engine can conventionally be equipped with a waste heat recovery system, i.e. a system making use of one or several heat sources produced by the vehicle operation, such as the hot exhaust gases which contain a lot of thermal energy that would otherwise be lost. Such a waste heat recovery system converts the heat energy into mechanical or electrical or physical energy or power. Some waste heat recovery systems operate thanks to a working fluid, distinct from the exhaust gases, which is heated by the exhaust gases, in a heat exchanger, and which is expanded in an expander where part of the energy of the working fluid is converted into mechanical energy.
One example of a waste heat recovery system is a circuit in which a working fluid flowing in a closed loop undergoes the following successive processes:                the working fluid, which is a liquid at this stage, is pumped from low to high pressure;        the high pressure liquid working fluid is evaporated in a heat exchanger by means of said heat source;        the gaseous working fluid is expanded in an expander where the energy of the working fluid is converted into mechanical energy;        finally, the gaseous working fluid is condensed.        
As a result, at least part of the thermal energy of the heat source used to evaporate the working fluid is recovered in the expander.
Such a waste heat recovery system can be, for instance, a Rankine system.
In order to increase the amount of energy that can be recovered, some conventional waste heat recovery systems include two heat exchangers arranged in parallel, namely:                a first heat exchanger which is arranged in a first line and is thermally connected to the exhaust line;        and a second heat exchanger which is arranged in a second line and is thermally connected to another line carrying a warm fluid. The warm fluid may be a fluid which is carried towards the engine, such as the EGR (exhaust gas recirculation) gases flowing in an EGR line. The warm fluid may be engine cooling fluid or a gearbox or engine lubricant fluid.        
WO 2012/009526 discloses a waste heat recovery system having a first line including a heat exchanger connected to the exhaust line, and a second line, arranged in parallel with the first line, including a heat exchanger connected to an EGR line.
In the case where the warm fluid flows in a closed loop in the engine arrangement, for example towards the engine, it may be advantageous that its temperature at the engine inlet is controlled to ensure the engine is operated efficiently. More specifically, it may be necessary that said temperature must be maintained below a predetermined value which can depend on the warm fluid function.
To that end, in some operating conditions in which said temperature of the warm fluid can be fairly high, the flow rate of the working fluid in the second line can be increased in order to provide more cooling capacity. However, as a result, the working fluid which exits the second heat exchanger may not be fully evaporated. Therefore, there is a risk that the working fluid, at the expander inlet, might still contain liquid, which could seriously damage the expander.
Several solutions are known to solve the above problem resulting from the coexistence of two contradictory constraints.
A solution consists in providing an additional cooler on the additional fluid line carrying the warm fluid, between the second heat exchanger and the engine. This solution is costly and may be not easy to implement because of the lack of space available to install additional components.
It is also known to provide a bypass of the expander. In this way, the expander can be by-passed when necessary, i.e. when the working fluid at the expander inlet is not fully gaseous. Although this solution solves the above mentioned problem, it is not fully satisfactory. Indeed, it implies that, in case the working fluid from the second line is not fully evaporated, no working fluid at all can flow through the expander. However, there are some operating conditions in which the working fluid from the first line can be fully evaporated whereas the working fluid from the second line is not. In such a case, no energy can be recovered at the expander when it could have been partly possible.
It therefore appears that engine arrangements comprising a waste heat recovery system are not fully satisfactory and could be improved.
It is desirable to provide an improved internal combustion engine arrangement comprising a waste heat recovery system which can overcome the drawbacks of the prior art engine arrangements.
It is desirable to provide such an engine arrangement which makes it possible to more efficiently use the thermal energy from both heat sources without impairing the engine arrangement overall efficiency nor damaging the expander.
According to a first aspect, the invention relates to an internal combustion engine arrangement which comprises:                an internal combustion engine;        an exhaust line capable of collecting exhaust gases from the engine;        an additional fluid line, distinct from the exhaust line, carrying a warm fluid;        a waste heat recovery system carrying a working fluid in a closed loop, in which said working fluid is successively pressurized from a low pressure circuit portion to a high pressure circuit portion by a pump, evaporated in the high pressure circuit portion, expanded in an expander from the high pressure circuit portion to a low pressure circuit portion, and condensed in a condenser in the low pressure circuit portion.        
This waste heat recovery system comprises a first and a second lines arranged in parallel in the high pressure circuit portion upstream of the expander, the first and second lines joining at a downstream junction point in the high pressure circuit portion upstream of the expander, wherein the first line comprises a first heat exchanger thermally connected to the exhaust line, in which the working fluid can be heated by means of the exhaust gases, and the second line comprises a second heat exchanger thermally connected to the additional fluid line, in which the working fluid can be evaporated by means of the warm fluid.
According to the invention, the internal combustion engine arrangement further comprises:                a first by-pass system designed to prevent not fully evaporated working fluid from the first line to flow through the expander;        a second by-pass system which connects the second line upstream of the downstream junction point, to the low pressure circuit portion, at a connecting point, for by-passing the downstream junction point and the expander.        
Thus, owing to the provision of two by-pass systems, the invention allows to make use of the working fluid from the first line to recover energy at the expander, any time it is possible, even if the working fluid from the second line cannot be used because it is not fully evaporated.
In other words, in contrast with the prior art, the invention provides two by-pass systems which can be fully or at least partly distinct, rather than one single and global by-pass system. As a result, the second by-pass system can be used independently of the first by-pass system, resulting in working fluid still flowing towards the expander from the first line.
With the invention, it is possible to make sure that only fully evaporated working fluid, or working fluid under superheated vapour form (i.e. at a temperature higher than its boiling temperature) can enter the expander to ensure a proper operation of the expander and prevent damaging it.
It has to be noted that, in embodiments where the two by-pass systems have some common parts, the first by-pass system might also prevent underheated working fluid from the second line to flow through the expander.
In practice, the first and second lines can be arranged in parallel between an upstream junction point to a downstream junction point. The upstream junction point can be located:                either in the high pressure circuit portion, i.e. downstream from the pump. Then, the first and a second lines are arranged in parallel between the pump and the expander, and a single pump can be provided;        or in the low pressure circuit portion. In this configuration, there may be provided one pump for each of the first and second lines, the upstream junction point being located upstream from the pumps.        
As regards the second by-pass system, it can connect a point of the second line located upstream of the downstream junction point and downstream of the second heat exchanger to the connecting point.
According to an implementation of the invention, the second bypass system can comprise at least one by-pass valve which may be arranged in the second line between the second heat exchanger and the downstream junction point and which may be configured for directing the flow of working fluid from the second heat exchanger either through the second line to the downstream junction point, or to the low pressure circuit portion.
For example, the second bypass system can be connected to the low pressure circuit portion upstream of the condenser.
The second bypass system can comprise a secondary line which by-passes the expander and connects the second line upstream of the downstream junction point to a connecting point located in the low pressure circuit portion between the expander and the condenser. As the secondary line by-passes the expander, it may have no common parts with the high pressure circuit portion and low pressure circuit portion.
According to an implementation of the invention, the engine arrangement comprises a determining device for determining at least one physical parameter of the working fluid in the second line, and a control unit operatively connected to the determining device for controlling the by-pass valve as a function of said physical parameter(s).
The physical parameter(s) can for example be determined in the second line, between the second heat exchanger and the downstream junction point.
The physical parameters are preferably those parameters allowing to determine whether the working fluid is fully evaporated or not, or allowing to determine the liquid content of the fluid. Said parameters can include temperature, pressure and flow rate.
The physical parameters, can either be measured by one or several dedicated sensors, or calculated using other values measured in the engine arrangement. Therefore, the second by-pass system can be activated when required, as a function of said physical parameters, eventually among other parameters.
In practice, if the working fluid is determined to be in a fully evaporated or superheated vapour state, the working fluid is directed towards the downstream junction point, and thus to the expander. On the contrary, if the working fluid is determined to be in a not fully evaporated state, this may result in the working fluid directed to the connecting point through the by-pass system.
According to an embodiment of the invention, the first by-pass system may comprise a first by-pass line having an inlet located between the first heat exchanger and the expander, and an outlet located in the low pressure circuit portion between the expander and the condenser. In practice, the first by-pass line can have an inlet located between the downstream junction point and the expander. In this embodiment, the first by-pass system allows the working fluid to by-pass the expander.
According to another embodiment of the invention, the first by-pass system may comprise a control valve which is arranged in the first line, upstream from the first heat exchanger, and which is capable of preventing the working fluid from flowing into the first heat exchanger. In this embodiment the first by-pass system allows the working fluid to by-pass the first heat exchanger. The control valve may for example be arranged at an upstream junction point of the first and second lines, thereby allowing regulating the sub flows of working fluid both in the first and second lines.
The engine arrangement may further comprise a control system for controlling the flow rate of working fluid in the second line, in order to regulate the temperature of the warm fluid in the additional fluid line, between the second heat exchanger and the engine.
To that end, according to an embodiment, the control system can comprise an electric motor capable of driving the pump, and a proportional three way valve designed to regulate the sub flow rates of the working fluid in the first and second lines. For example, the proportional three way valve can be located at an upstream junction point of the first and second lines. Providing an electrically driven pump makes it possible to control the global flow rate of working fluid in the loop, while the proportional three way valve makes it possible to control the sub flows of working fluid in the first line and in the second line.
In another embodiment, the pump can be mechanically driven by the internal combustion engine, the control system comprising an additional proportional three way valve located between the pump and the second heat exchanger and having a port connected to the low pressure circuit portion, between the condenser and the pump, through a return line. In this embodiment, the global flow rate of working fluid in the closed loop cannot be regulated. The additional proportional three way valve, by directing the appropriate flow mass of working fluid directly back to the low pressure circuit portion upstream from the pump, possibly in a tank, makes it possible to control the global flow rate of the working fluid. In combination with a proportional three way valve located at an upstream junction point between the first and second lines, the sub flow of working fluid in the second line can be controlled.
According to a second aspect, the invention relates to a process for controlling a waste heat recovery system forming part of an internal combustion engine arrangement. The process comprises:                collecting exhaust gases from an internal combustion engine in an exhaust line;        carrying a warm fluid in an additional fluid line, distinct from the exhaust line;        carrying a working fluid in a closed loop, in which said working fluid is successively pressurized, evaporated, expanded in an expander to convert energy of the working fluid into mechanical energy or power, and condensed, wherein the working fluid is divided into a first flow heated by the exhaust gases and into a separate second flow heated by the warm fluid.        
The process can further comprise determining at least one physical parameter of the working fluid in the first flow; and determining at least one physical parameter of the working fluid in the second flow.
According to an embodiment of the invention, if the first fluid flow is determined to be in a first fluid state and the second fluid flow is determined to be in a second fluid state, the process comprises controlling a first bypass system so that the first fluid flow is expanded in the expander and controlling a second bypass system so that the second fluid flow by-passes the expander.
According to another embodiment of the invention, if the first fluid flow is determined to be in a first fluid state and the second fluid flow is determined to be in a second fluid state, the process comprises                determining if mixing of the first flow with the second flow would result in the resulting mixed flow being in a first state;        and, if so, controlling a first bypass system and a second bypass system so that the first fluid flow is mixed with the second fluid flow and so that the resulting mixed flow is expanded in the expander.        
Furthermore, if the first fluid flow is determined to be in a first fluid state, the process can comprise:                controlling the first by-pass system so that the first fluid flow bypasses the expander;        or controlling the first by-pass system so that the flow rate of the first fluid flow is zero. In other words: no working fluid flows through the first heat exchanger.        
In practice, the first fluid state can be one of a fully evaporated and a superheated vapour state, while the second fluid state can be a not fully evaporated state.
The invention can provide a process which comprises:
a) determining at least one physical parameter of the working fluid in the first line and, in case said physical parameter indicates that the working fluid in said first line is in a first fluid state—i.e. not fully evaporated or not superheated vapour—preventing said working fluid from flowing through the expander;
b) determining at least one physical parameter of the working fluid in the second line and controlling a second by-pass system which connects the second line upstream of the downstream junction point to the low pressure circuit portion as a function of said physical parameter, so as to direct the flow of working fluid from the second heat exchanger either through the second line to the downstream junction point, or through a secondary line, that is distinct from the common line, to the low pressure circuit portion for by-passing the downstream junction point and the expander.
in order to prevent not fully evaporated working fluid from flowing through the expander.
Actions a) and b) are not successive steps, but actions that can be independently performed in order to avoid that a still partly liquid working fluid enters the expander.
Therefore, as regards action a), having a not fully evaporated working fluid in the first line, downstream of the first expander, will entail the activation of the first by-pass system. As regards action b), the expander is bypassed depending on the physical parameter(s) of the working fluid in the second line, downstream of the second expander, to ensure the working fluid entering the expander will be fully evaporated or superheated vapour.
According to an implementation, in action b), the working fluid can be directed through the secondary line in case it is determined that said working fluid, in the second line, is not fully evaporated.
According to another implementation, in case, in action b), it is determined that said working fluid, in the second line, is not fully evaporated, the process can further comprise:                determining if the physical parameters of the working fluid in the first line are sufficient to cause the full evaporation of the working fluid from the second line around the downstream junction point;        and, if so, directing the flow of working fluid from the second heat exchanger through the second line to the downstream junction point.        
These and other features and advantages will become apparent upon reading the following description in view of the drawing attached hereto representing, as non-limiting examples, embodiments of a vehicle according to the invention.